Electrostrictive or piezoelectric actuator device

Abstract

An electrostrictive or piezoelectric actuator device includes a solid state actuator element (4) that is elongated in the lengthwise direction (L) and contracted in the transverse direction (T) upon application of an electric voltage thereto. The actuator element (4) is clampingly held between a housing floor and an actuator output pin (6) in a housing (2). A protective interlayer (12) is respectively arranged between the lengthwise end faces of the actuator element (4) and the housing floor and the actuator pin respectively, to protect the actuator element against transverse stress peaks. The interlayer (12) provides a soft or elastic coupling in the transverse direction and a substantially rigid, force and stroke transmitting coupling in the lengthwise direction. To achieve this, each interlayer (12) is made of a material having an anisotropic modulus of elasticity with a lengthwise stiffness that is considerably higher than that of the solid state material of the actuator element and a transverse stiffness that is less than that of the solid state material of the actuator element.

What is claimed is: 
     
       1. An actuator device comprising: an actuator body;   a solid state actuator element comprising a solid state material and having a length in a lengthwise direction that is adapted to be variable responsive to an electrical voltage being applied to said actuator element, wherein said actuator element has two respective ends that are coupled in a force transmitting manner to said actuator body; and   at least one protective interlayer arranged between at least one of said ends of said actuator element and said actuator body, wherein said protective interlayer comprises an anisotropic material having an anisotropic modulus of elasticity with a relatively greater lengthwise stiffness in said lengthwise direction and a relatively lesser transverse stiffness in a transverse direction perpendicular to said lengthwise direction.   
     
     
       2. The actuator device according to claim 1, wherein said at least one protective interlayer is adapted to reduce peak transverse loads acting in said transverse direction on said solid state actuator element adjacent said at least one end thereof. 
     
     
       3. The actuator device according to claim 1, comprising two of said protective interlayers arranged respectively between said two ends of said actuator element and said actuator body. 
     
     
       4. The actuator device according to claim 1, wherein a stiffness of said solid state material is between said transverse stiffness and said lengthwise stiffness of said anisotropic material. 
     
     
       5. The actuator device according to claim 4, wherein said solid state material is an electrostrictive material. 
     
     
       6. The actuator device according to claim 4, wherein said solid state material is a piezoelectric ceramic material. 
     
     
       7. The actuator device according to claim 4, wherein a ratio of said lengthwise stiffness relative to said transverse stiffness is greater than 10. 
     
     
       8. The actuator device according to claim 7, wherein said ratio is at least 30. 
     
     
       9. The actuator device according to claim 7, wherein said stiffness of said solid state material is within ±10% of the geometric mean of said lengthwise stiffness and said transverse stiffness. 
     
     
       10. The actuator device according to claim 1, wherein said anisotropic material of said protective interlayer is a fiber-reinforced composite material comprising fibers with a unidirectional orientation parallel to said lengthwise direction. 
     
     
       11. The actuator device according to claim 10, wherein said composite material is a carbon fiber-reinforced composite material. 
     
     
       12. The actuator device according to claim 10, wherein said protective interlayer consists entirely of said fiber-reinforced composite material. 
     
     
       13. The actuator device according to claim 1, wherein a ratio of said lengthwise stiffness relative to said transverse stiffness is greater than 10. 
     
     
       14. The actuator device according to claim 13, wherein said ratio is at least 50. 
     
     
       15. The actuator device according to claim 1, wherein said lengthwise stiffness is greater than 300 GPa, and said transverse stiffness is less than 10 GPa. 
     
     
       16. The actuator device according to claim 1, wherein said protective interlayer does not comprise a piezoelectric material. 
     
     
       17. The actuator device according to claim 1, wherein said solid state material is a piezoelectric material, said solid state actuator element comprises stacked layers of said piezoelectric material, and said protective interlayer is a solid pressure plate of said anisotropic material coupled to said actuator element over an entire surface area of said at least one end of said actuator element. 
     
     
       18. The actuator device according to claim 1, wherein said protective interlayer is surfacially bonded to said at least one end of said actuator element. 
     
     
       19. The actuator device according to claim 1, wherein said actuator body comprises a housing and an actuator pin movably arranged relative to said housing so as to protrude a variable extent from said housing, and said actuator element is arranged within said housing with a first one of said two ends coupled in a force transmitting manner to said housing and a second one of said two ends coupled in a force transmitting manner to said actuator pin. 
     
     
       20. The actuator device according to claim 19, further comprising a biasing spring arranged to bias said actuator pin relative to said housing against said actuator element, so as to clampingly hold said actuator element in a pre-compressed state between said actuator pin and said housing.